OK then,..just to Help on the Magnet and Heat thing a bit,..lol
All magnetic materials are at all times as fully magnetized as their thermal state permits.
Prior to "magnetization" their magnetic domains arrange randomly to minimize their internal (and external) energy state.
Magnetization rotates magnetic domains into common alignment. Permanent magnets retain this alignment to a degree, depending on their geometry, chemistry and anisotropy mechanisms. (Consider anisotropy here as all those things that resist a magnetizing force, and thus a demagnetizing force as well).
Magnetic domains in the center of a magnet support each other, but those domains closer to the sides, ends and edges of the geometry have less support, and some are reversed by the magnet's own external field, which has a polarity opposite to the internal field.
When heat is applied, longer electron orbits cause all domains to weaken to a degree, and those with more exposure to the external field (or are weaker for some other reason) will also reverse.
Invariably, magnet manufacturers further Heat Treat the Various materials during manufacture, to Better suit it's designed operating environment, through a process known as 'Thermal Knockdown'.
Thermal knockdown is the process of raising a magnet’s temperature to the temperature expected in the application so any impending change will have occurred prior to installation of the magnet. At elevated temperatures, the demagnetizing force for isolated magnets will be its own self demagnetizing force, so thermal stabilization is invariably done in a fixture that reproduces the operating 'permeance coefficient',..(gotta Love that term eh!!??), to avoid loss of useful and stable flux levels.
A magnet is heat stabilized by exposing it to elevated temperatures for a specified amount of time.
This is done to prepare for the irreversible losses of magnetism that most magnets experience when exposed to elevated temperatures.
You can think of heat stabilization as insurance against elevated temperatures.
There are two types of magnetic losses when a magnet is heated to elevated temperatures: reversible & irreversible.
Reversible magnetic loss is the weakening of a magnet when heated to elevated temperatures. It is called reversible, because the magnet recovers this portion fully upon returning to room temperature.
Irreversible magnetic loss also occurs at elevated temperatures but is not recovered upon return to room temperature. It is a permanent loss, unless the magnet is sent back for remagnetization. This is a one-time-only effect.
An example: A given magnet produces 1000 Gauss at room temperature. It is baked at 200 °C (400 °F). While at that temperature, it only produces 850 Gauss. Upon return to room temperature you measure it and find it now only produces 950 Gauss. The missing 50 Gauss is the irreversible loss. If the magnet was returned to 200 °C, it will still produce 850 Gauss. If it was taken to a higher temperature then it would lose more output.
The amount of irreversible loss depends on a lot of factors, including the type of magnetic material, the shape of the magnet, the temperature it experiences and the amount of time it sees that temperature!!
Ceramic Magnets are definitely the most 'delicate' in that regard, as depending on the material used, their 'absolute', or Curie point, can be as low as 200 deg' C, but usually around 300 to 350 deg' C and often do Not exhibit the same kinds of Natural 'Anisotropy' as Rare Earth materials.
All magnetic materials follow a fairly Linear curve of megnetic coercivity as the temperature rises and falls, in Fact Most Magnets get noticeably Stronger when cold! (Ceramic magnets being the exception here!),..in Fact it is THIS fact, that has made Neo-Dymium, style 'Martixes', such as that developed by AC Delco for use as Starter Motors, such a Great thing for the Auto Industry. Want some Cranking Power in The Snow !!???,..lol
Neo type materials exhibit even Greater Coercivity at Low tepmeratures than Cobalt, but unfortunately, do Not exhibit similar stability as Cobalt at Higher temperatures,..Mind you the Thing with Neo's, is that their Inherent Heat stability can be Extremely High, so even though they Lose coercivity at elevated temperatures, they invariably Return, (without Loss), unless taken Past their Curie point.
Hey!,..I kinda figured You'd Know all this Jacco !!!,..
I guess, when you consider that Open Motors have often become hot enough to Melt Lead Wires Off, allow Pinions to spin, magnet holding epoxy to soften, let alone complete de-stabilisation and Frying of Cummutators and armarures!!!,..lol,..the Heat applied when Soldering in a Motor, when well Prepared with Good Flux and a Damn Hot Iron, is in Fact Rather 'Breif' !! and if Done Quickly and 'Deftly', is Less of a Problem than one would Imagine.
So, as noted from the Above, Ceramic magnet Motors should be Treated with Far Greater Care 'Heat Wise', (they also Don't like being Dropped!) and I would Venture, would 'Benefit' from Regular and reliable Re-Magnetisation, to maintain Optimal performance !!
